An imaging system may include an interactive display surface, which may be a surface for displaying computer generated output and receiving interactive input from a user manipulating one or more objects on or above the interactive display surface. Such an imaging system may be directly illuminated with light such that a camera may capture an image of the interactive display surface and the one or more objects on or above the interactive display surface. Bright ambient light may cause an image to appear washed out to the camera unless a level of direct illumination is increased to offset an effect of the bright ambient light.
One possible solution to this problem is to have the interactive display surface illuminated by a constant bright level of direct illumination. However, a drawback to this approach is that the imaging system will use more power to keep the direct illumination operating at a high level. Further, a constant bright level of illumination may result in a higher level of heat generated by a light source, such as one or more light bulbs or light emitting diodes (LEDs). In addition, the light source may have a shorter life expectancy when always operated at a bright setting.
In imaging systems that respond to visible light, the visible light projected by the systems to produce images may be partially reflected back by the interactive display surface, thereby leading to false readings. Even if such reflections could be suppressed, unless the imaging systems were disposed in a dark room, room light and other visible light passing through the interactive display surface would adversely affect such imaging systems. Furthermore, such imaging system could not produce dark or dim screens because there either would not be sufficient visible light to detect objects and movements, or the light used to detect objects and movement would eclipse the dark or dim images intended for the user to see. The use of non-visible light, such as, for example, ultraviolet (UV) light or infrared (IR) light, to detect objects placed on an interactive display surface can avoid some of the problems that would arise from attempting to recognize objects with visible light.
In an imaging system that uses non-visible light, such as infrared or ultraviolet light, to directly illuminate an interactive display surface for a camera that is sensitive to the non-visible light, a constant high level of direct illumination for overcoming a possible high level of non-visible ambient light may be detrimental to eye safety in addition to the problems mentioned above.
Human eyes respond to visible wavelengths of light. When visible light is bright, a pupil of the human eye will contract and permit less light to enter the eye. When visible light is dim, the pupil of the human eye will dilate and permit more light to enter the eye. However, if a level of visible light is dim and a level of non-visible light is bright, the pupil of the human eye will dilate to permit more visible light as well as more harmful non-visible light to enter the eye.